The orientation of the constituents of webs or sheets should be of such a degree and direction as are suited to their intended use. Therefore, the orientation of the constituents of sheets or the like should be suitably and readily checked up during or after production.
For example, in the case of a fiber sheet such as paper, to obtain a high quality it is important to disperse fibers sufficiently to obtain as low as concentration as possible and then screen them for paper making. However, the viscosity force of paper stock developed when the stock is spouted at high speed from the head box or the dragging force exerted on the paper stock by the wire cloth, on which it is carried, traveling at a speed almost equal to the flow rate of stock causes the fibers to be oriented in the direction of flow, thus producing differences in paper strength and gloss between longitudinal and transverse directions. Particularly, if during operation the operator makes a mistake in setting the slice flow collision position, the positional relation between the breast roll, wire cloth and forming board or other operating conditions, abnormally varient orientations of fibers take place, imparting a great deal of anisotropy to the paper, which, in turn, forms a cause of frequent break of paper at the wet end or marked ununiformity of coating color profile when a coating color is applied to the paper by a coater.
Further, in the phase of final product, since dimensional changes due to variations in the humidity of the atmosphere are irregular, curls and wrinkles are formed.
Conventionally, to detect such abnormality of fiber orientation in its early stage, a sample of paper is taken at the reel part of the paper making machine as soon as the paper roll is wound up and the sample is tested for the presence or absence of abnormality of fiber orientation as by measurement of zero-span tensile strength (TAPPI, STD, T 481 sm-60), ultra-sonic method, X-ray diffraction method, or viscoelectricity spectroanalysis. Such methods, however, involve a troublesome procedure for setting a sample strip such as a sheet or a sample portion in the measuring mechanism and take a long time in ascertaining the abnormality of fiber orientation. Thus, if there is an abnormality, a large amount of reject would be produced until the completion of a check of fiber orientation over the entire width of the machine, particularly a modern machine which has been sped up and increased in width.
Plastic sheets will now be considered. In the production of plastic sheets, a non-stretched sheet is produced either by the tubular film process in which the sheet material is first heated or frictionmelted to be given fluidity and then extruded into a cylindrical form, into which air is blow to inflate it and at the same time is externally cooled for solidification or by the T-die process in which the melt is extruded into a smooth thin film form and then cooled for solidification in a water tank or on a cooling drum. However, such non-stretched sheet is too inferior in such mechanical strengths as tensile strength, impact strength and tear strength and in processability to be used as such. Thus, to obtain a sheet of good quality, the non-stretched sheet is heated to a suitable temperature above its softening point or below its melting point and subjected to uniaxial or biaxial stretching to improve its physical properties. In such stretching process, it does not necessarily follow that simple mechanically stretching the nonstretched sheet provides a sheet of good quality, but it is necessary that the stretching be performed to provide a particular orientation of molecules to agree with the intended use of the sheet product.
Further, a consideration will be given to a ceramic sheet. In production, a fine ceramic powder is mixed with a binding agent and a lubricant to produce a slip, which is then poured onto a continuously traveling tape of polyethylene or Teflon, and after the thickness of the slip layer on the tape is adjusted as by a doctor, it is fired and finished, the process being called the tape casting forming method, whereby a ceramic sheet in thin film form is obtained. Such thin film-like ceramic sheets are used as a material for laminated ceramic capacitors, for example, by laminating them alternately with electrodes. For the application of ceramic sheets to such use, it is of utmost importance from the standpoint of securing the quality of capacitors at high level that the dielectric constant across the width of ceramic sheets be substantially uniform. Therefore, a checkup of widthwise molecular orientation corresponding to dielectric constant must be made so that only those ceramic sheets which are appropriate may be used. Therefore, said plastic films and ceramic films must be tested for their molecular orientation as in the case of fiber sheets. Thus, conventionally, in these sheets, as soon as the roll is wound up at the winder part of said stretching machine or tape casting forming device, a sample is taken and tested for the presence of absence of abnormality of molecular orientation as by elastic modulus measurement, X-ray diffraction method, or infrared absorption spectroanalysis. With these methods, however, there is the same drawback as was previouly described in connection with paper sheets, that is, a large amount of reject would be produced before the completion of the checkup of molecular orientation of the sheet product across the entire width of the processing machine.
With the above in mind, we have conducted an intensive study with a view to developing an apparatus which is easy to handle and capable of making measurements in a short time. In this connection, in order to ascertain the orientation state of the constituent, i.e., fibers or molecules of a sheet, we have investigated the use of and experimented with a microwave of a nature attenuating in accordance with the presence of molecules and we have found that if linearly polarized microwaves (hereinafter reffered to as linearly polarized waves) are applied, at right angles, to the sheet surface while relatively rotating the sheet in its plane, the amount of attenuation increases or decreases with the rotative and that the angle at which the maximum amount of attenuation is exhibited coincides with the direction of orientation of fibers or molecules.
In the case of a fiber web or sheet such as paper, the attenuation of microwaves associated with the orientation of fibers takes place not because of the fibers themselves but in that the microwaves are absorbed by H.sub.2 O molecules which are contained in the fibers and which have an orientation corresponding to the orientation of fibers. In addition, where the moisture content of fiber sheets is about 15% or above, H.sub.2 O molecules which adhered to the fiber surfaces in agreement with the orientation of fibers by hydrogen bond or by capillarity when the moisture content was below said value, begin to adhere to the fibers independently of the orientation of fibers, so that the orientation of H.sub.2 O molecules in the fiber sheet is decreased to a marked degree. For this reason, the method of the present invention is applied to fiber sheets whose moisture content is less than 15%.
The principle of the invention, in a sample model based on the following equation, is supported by the assumption that where fibers or molecules of a sheet are oriented at an angle .theta. from the x-axis, the amount of attenuation is at a maximum in a plane of polarization of microwaves where .theta.=.phi.. ##EQU1## .DELTA.W: Amount of attenuation of microwaves N: Number of molecules per unit volume, those molecules being capable of microwave-induced movement and including H.sub.2 O molecules contained in fibers; hereinafter the same
.mu.: Effective dipole moment of molecules PA0 .theta.: Angle between dipole moment of molecules and x-axis PA0 .phi.: Angle of plane of polarization of waves measured counterclockwise from x-axis PA0 k: Boltzman's constant PA0 T: Absolute temperature PA0 C.sub.1, C.sub.2 : Constants. PA0 inserting a sample portion of said web or sheet product into said small clearance, PA0 emitting linearly polarized microwaves from said transmitting antenna toward said open ends to allow them to fall on the surface of said sample portion at right angles thereto while producing a relative motion betwen the plane of polarization of microwaves and said sample portion around the axis of said cavity resonator, PA0 receiving the microwaves guided from the waveguide disposed on the transmitting side via the sample portion in said clearance to the waveguide disposed on the receiving side so as to find the amount of microwaves absorbed by said sample portion, and PA0 determining the orientation of the constituents of said web or sheet product from the angular position of said sample portion, where said amount of absorption is at a maximum, relative to said plane of polarization.